Identifying to which page/spread a book has been open is very useful since it allows selective interaction with the user of the book depending on the content of the particular page/spread. One application that is particularly popular with board books for children involves an audio/visual presentation to the user of the book. In this case, the opening of the book to a particular spread can trigger recorded pronunciation of the name of a displayed object, recorded reading of a text displayed on the page, recorded song or other audio/visual effects associated with the content of the pages of the spread.
Various systems for page/spread identification have been developed. One system (U.S. Pat. No. 6,763,995 to Song) includes magnetic signature sensors configured to detect the magnetic signature of the pages as they are turned. The system is bulky and involves magnets inserted in pages, which is a safety hazard with small children. Another system (U.S. Pat. No. 5,803,748 and U.S. Pat. No. 6,041,215 to Maddrell et al.) relies on user applying a pressure on pressure sensitive switches inserted in passageways within the leaves of the book. Further system (U.S. Pat. No. 6,491,220 to May) employs flexible sensors affixed to each sheet to identify interaction of the user with the sheet. Another system, suggested by Li in U.S. Pat. No. 5,631,883, includes identification labels attached to the edge of the pages. A contact plate is depressed to contact an identification label and trigger identification of the corresponding page. Systems, using external optical devices to read identification codes printed on each page have also been suggested (U.S. Pat. No. 6,729,543 to Arons et al.)
The arrangements in the above systems are either somewhat complex ((U.S. Pat. No. 6,763,995; U.S. Pat. No. 6,491,220 and U.S. Pat. No. 6,729,543) or require user's participation in identifying the pages (U.S. Pat. No. 5,803,748, U.S. Pat. No. 6,041,215 and U.S. Pat. No. 5,631,883).
Accordingly, it would be preferable if a simple and reliable system for spread identification is designed that is triggered automatically upon opening of the book to a particular spread.